(1) Field of the Invention
This invention relates to a self-contained breathing assembly, and more particularly to an improved positive pressure self-contained breathing assembly for temporary use by a wearer in a noxious environment, such as is worn by a firefighter and including a remotely positioned pressure demand regulator as well as an improved face mask interconnect assembly.
(2) Description of the Prior Art
Self-contained breathing assemblies (SCBA's) are worn by industrial workers, and in particular firefighters, to provide a safe, respirable breathing condition while the user works in a hostile environment. Currently, breathing performance and service life rating of such apparatus are based upon user consumption at the rate of 42 liters per minute, wherein inhalation and exhalation reach peaks instantaneous flow rates of about 115 liters per minute. For firefighting duty, the National Fire Prevention Administration (NFPA) has defined new performance standards in its Standard No. 1981 (for open circuit SCBA's) wherein peak instantaneous breathing rates exceed 400 liters per minute.
Such demand regulators must be highly responsive to meet the constantly-changing pattern of human respiration and peak instantaneous flow rates of up to 400 liters per minute. Pressure-demand regulators create a positive pressure in the user's face mask throughout the respiration cycle while concomitantly providing flow corresponding to the user's demand, such as disclosed in U.S. Pat. No. 4,334,532 to Jackson. Such a pressure-demand regulator normally maintains a positive pressure of about 0.5 to 1.5 inches water-column height under static conditions (when the user is not breathing) and does not permit the face mask pressure to become negative at peak flow rates of up to 400 liters per minute.
The demand regulator may be mounted on the face piece to provide an almost instantaneous response to the user's respiratory demand, however the bulkiness restricts vision and can restrict head movement resulting from its size and hose coupling requirements. Conversely, in known designs, the regulator's response time decreases considerably if the regulator is located a distance from the facepiece, and the two are joined by a large diameter flexible tube, although the remotely located regulator affords unencumbered vision and head movement.
One problem with demand regulators used in debris-ridden and/or subfreezing environments, routinely encountered in firefighting, is that the regulator's operation may be hindered by ice and/or debris. Additionally, any debris entering the breathing tube or regulator before the face mask is donned can be blown into the wearer's face during use. One solution to this problem is the provision of a cap to be manually positioned over the regulator outlet after use.
A further problem for any pressure demand regulator is the continued flow of gas when the regulator is disconnected from the facepiece since the regulator will continue to flow to try to create a positive pressure.